Inhibitors of Apoptosis Proteins (IAPs) are naturally occurring intra-cellular proteins that suppress caspase-dependent apoptosis. SMAC, also known as DIABLO, is another intracellular protein that functions to antagonize, i.e., inhibit the activity of IAPs. In normal healthy cells, SMAC and IAPs function together to maintain healthy cells. However, in certain disease states, e.g., cancers and other proliferative disorders, IAPs are not adequately antagonized and therefore prevent apoptosis and cause or exacerbate abnormal proliferation and survival.
SMAC mimetics, also known as IAP antagonists, are synthetic small molecules that mimic the structure and IAP antagonist activity of the four N-terminal amino acids of SMAC. (SMAC mimetics are sometimes referred to as IAP antagonists.) When administered to animals suffering proliferative disorders, the SMAC mimetics antagonize IAPs, causing an increase in apoptosis among abnormally proliferating cells. Examples of SMAC peptidomimetics are those disclosed in U.S. Pat. No. 7,517,906; U.S. Pat. No. 7,309,792; U.S. Pat. No. 7,419,975; US 2005/0234042; US 2005/0261203; US 2006/0014700; US 2006/0025347; US 2006/0052311; US 2006/0128632; US 2006/0167066; US 2007/0042428; US 2007/032437; US 2008/0132485; WO 2005/069888; WO 2005/069894; WO 2006/010118; WO 2006/122408; WO 2006/017295; WO 2006/133147; WO 2006/128455; WO 2006/091972; WO 2006/020060; WO 2006/014361; WO 2006/097791; WO 2005/094818; WO 2008/045905; WO 2008/016893; WO 2007/136921; WO 2007/021825; WO 2007/130626; WO 2007/106192; and WO 2007/101347.